Ultra High Pressure Treatment Of ‘Xuehua' Pear Juice Optimization And Quality Change During Storage

‘Xuehua' pear is fragrant and beautiful,and rich in protein,minerals,vitamins and other nutrients.‘Xuehua' pear juice is especially popular with consumers,but the current high-temperature sterilization has a great impact on its nutrition and aroma components.As the most potential cold sterilization technology,ultra-high pressure technology has important application value in the production of ‘Xuehua' pear juice.In this experiment,‘Xuehua' pear juice was used as raw material,The effects of single factors such as treatment pressure,pressure holding time,pressure times and initial pH value on the physicochemical indexes and microbial safety of fruit juice were studied.On this basis,the ultra-high pressure sterilization process was optimized by response interview;The changes of microorganisms,physical and chemical indexes and volatile components of ultra-high pressure(UHP)pear juice during storage at different temperatures were analyzed.The results are as follows:1.Taking ‘Xuehua' pear juice as the research object,the process conditions of ultra-high pressure treatment were optimized by single factor and response surface test.The optimum process was as follows: the initial pH value of pear juice was 4.3,the ultra-high pressure treatment pressure was 480 Mpa and the treatment time was 16 min.Under these conditions,the color of pear juice was light yellow,with the aroma of snow pear itself,moderate acidity and sweetness,good taste,and the comprehensive score was 9.05 points.2.The changes of physicochemical indexes and microbial indexes of ultra-high pressure treated fruit juice during storage at 25 ? and 4 ? were analyzed.The results showed that the total number of colonies and the detection rate of mold and yeast in ‘Xuehua' pear juice after ultra-high pressure treatment were 0.The content of soluble solids(SSC),total phenols,flavonoids,DPPH free radical scavenging ability and polyphenol oxidase(PPO)activity were lower than those in the original juice.UHP pear juice and untreated pear juice(CK)were stored at different temperatures.At 25 ?,SSC,pH,titratable acid and turbidity in UHP group were relatively stable;The values of L and a did not change significantly,but the value of b increased;After 20 days of storage,the total number of colonies,molds and yeasts were not detected;However,total phenols,flavonoids,DPPH radical scavenging ability and PPO enzyme activity decreased.In CK group,bag swelling occurred after storage for 3 days.At 4 ?,the indexes of UHP group and CK group showed a downward trend.30 days before storage,they both decreased gently,and there was no significant difference;However,after 30 days of storage,the indexes of CK group and UHP group began to show significant differences,SSC and pH increased significantly,and titratable acid and turbidity decreased significantly;Microorganisms were not detected in UHP group during storage,but swelling bags appeared in CK group after storage for 60 days and were not edible.3.Analysis of flavor changes of pear juice treated with ultra-high pressure during storage by gas chromatography-mass spectrometry(GC-MS)combined with electronic nose / electronic tongue.A total of 90 volatile substances were detected by GC-MS,including esters,aldehydes,alcohols,ethers,ketones,alkanes and olefins.At 25?,there were significant differences in esters and alcohols between UHP group and CK group,and the types and contents of alcohols increased significantly.At 4?,the types of esters decreased in UHP group,but the contents of ethyl caproate and ethyl butyrate were significantly higher than those in CK group.Electronic nose analysis showed that nitrogen oxides,methane,sulfide,terpenes,alcohols and some aromatic compounds were significantly distinguished during storage;Electronic tongue analysis showed that the acidity of CK group increased at 25?,but there was no significant difference between CK group and 4?.This study found that ultra-high pressure treatment combined with low temperature(4?)could better maintain the SSC,titratable acid,pH value,total phenol and flavonoids content of‘Xuehua' pear juice,stabilize the turbidity and color of pear juice,maintain high scavenging capacity of PPO and DPPH free radicals,and no microbial indexes were detected after 60 days of storage.It provides reference data for the application of non thermal processing in fruit juice and the ultra-high pressure treatment of ‘Xuehua' pear juice.